The emphasis of many laboratories has been to find either a micro- organism or an auto-antibody in their investigation of uveitis. Experiments recently performed by our laboratory have shown that cellular immunity plays a role in the pathogenesis of chronic or recurrent corneal disease. Cell-mediated immunity to ocular tissue, but not to the etiologic virus was clearly demonstrated by the migration inhibition technique. Humoral antibody to ocular or viral antigens did not correlate with the state of the disease. We are currently studying another mediator of cellular immunity lymphotoxin to confirm that cell- mediated responses are responsible for the chronicity of viral keratitis. The techniques to study cellular immunity have been well established in our laboratory. We, therefore, propose to study other ophthalmic conditions in particular uveitis, applying strict experimental standards. Our principal objective is to determine the role of cell-mediated, as well as humoral immunity in uveitis of unknown etiology. We shall also study uveitis in patients in whom an etiologic agent has been detected to determine whether, as in keratitis, the inital infection or the subsequent immune reactions are more important in the chronicity of the disorder. Such understanding should lead to better therapy and give direction to the search for new methods of treatment.